.THE ASH OF PLANTS. 129 



CaCOs + 2 HCl = CaClj + HjCOa and HjCOs = H,0 + COr 



Carbon dioxide is also termed anhydrous carbonic acid, 

 or again, carbonic anhydride. 



Cyanogen, Syjn. CjNj This important compound of Carbon and Ni- 

 trogen is a gas which has an odor like that of peaoh-pits, and which 

 burns on contact with a Ughted taper with a iine purple flame. In its 

 union with oxygen by combustion, carbon dioxide is formed, and nitro- 

 gen set free : 



CjNj + 4 = 2 COj 4- Nj. 



Cyanogen may be prepared by heating an Intimate mixture of two 

 parts by weight of ferrocyanide of potassium (yellow prusslate of 

 potash) and three parts of corrosive sublimate. The operation may 

 be conducted in a test-tube or small flask, to the mouth of which is 

 fitted a cork penetrated by a narrow glass tube. On applying heat, the 

 gas issues, and may be set on fire to observe its beautiful flame. 



Cyanogen, combined with iron, forms the Prussian blue of com- 

 merce, and its name, signifying the blue-prodticer, waagiven to it from 

 that circumstance. 



Cyanogen unites with the metallic elements, giving rise to a series 

 of bodies which are tenned Cyanides. Some of these often occur in 

 small quantity in the ashes of plants, being produced in the act of 

 burning by the union of nitrogen wltb carbon and a metal. For this 

 result, the temperature must be very high, carbon must be in excess, 

 the metal is usually potassium or calcium, the nitrogen may be either 

 free nitrogen of the atmosphere or that originally existing In the 

 organic matter. 



With hydrogen, cyanogen forms the deadly poison hydrocyanic or 

 prussic acid, HCy, which is produced from amygdalin, one of the ingre- 

 dients of bitter almonds, peae)i, and cherry seeds, when these are 

 crashed in contact with water. 



When a cyanide is brought in contact with steam at high tempera- 

 tures, it is decomposed, all its nitrogen being convei-ted into ammonia. 



Cyanogen is a normal Ingredient of one common plant. The oil of 

 mustard is allylsulphocyanaie, CjHjCNS. 



SULPHUR AND ITS COMPOUNDS. 



Sulphur, Sym. S, at. wt. 33. — The properties of this 

 element haye been already described (p. 25). Some of 

 its compounds have also been briefly alluded to, but re- 

 quire more detailed notice. 



Htdkogen Sulphide, Sym. HjS, mo. wt. 34. This substance, familiarly 

 known as sulphuretted hydrogen, occurs dissolved in the water of nu- 

 merous so-called sulphur springs, as those of Avon and Sharon, N. T., 

 from which it escapes as a fetid gas. It is not unfrequently emitted 

 from volcanoes and fumaroles. It is likewise produced In the decay of 

 organic bodies which contain sulphur, especially eggs, the Intolerable 

 odor of which, when rotten, Is largely due to this gas. It Is evolved 

 from manure heaps, from salt marshes, and even from the gpll of mpisf 

 meadows. 



9 



